Rolling of rod stock



Oct. 7, 1969 D. B. wooDcocK ETAI- ROLLING op Ron STOCKr Filed Dec. 9,1966 5 Sheets-Sheet l /IS 22 1 17a a '99 9a IMVEMTOQS;

DDNRLD Efwdn meemaak EDN/mj) LJILLIQMS I Oct. 7, 1969 D. B. wOODcOcKETAL 3,470,722

ROLLING 0F ROD STOCK Filed Dec. 9, 1966 5 Sheets-Sheet A (STAND) p2 t P5LOAD P (sTIFFNEss I CONTROL uNITsV-Srq SH 2 P I ROLLWAY DIMENSION I"A(5TAND BISTIFFNESS I CONTROL UNIT) LODAD c (COMBINED) Y ab l a7 P7 l Ii ROLLWAY DIMENSION V l @I mi www odi. 7, 1969 D, 5, WOQDCOCK ETAL3,470,722

ROLLING 0F ROD STOCK 5 Sheets-Sheet 3 Filed Dec. 9, 1966 Oct. 7, 1969ROLLING OF ROD STOCK 5 Sheets-Sheet 4 Filed D60. 9, 1966 m Mm if Nm om m@N l M \\X\ E@ 1.. O1l4/Ill.. L mw \\v\\\ \\\\..r l, \onv ww mv m Uv omm N iN N Nv wn Ow @n vm om n n Nm mm/ m Om, N O N UN A JM J 0 N E n N my ,k s 2 om o@ 5 woompd( United States Patent O U.S. Cl. 72-245 15Claims ABSTRACT OF THE DISCLOSURE A piston-andcylinder device with achamber containing a hydraulic uid or a rubber block is interposedbetween the head screws and the upper bearing assemblies, or between theupper and lower bearing assemblies, of the stands of a rolling mill todecrease or increase the effective stiffness of the stands and therebyto control the dimensional tolerances of the rolled product.

This invention relates to the rolling of rod stock in rolling mills(hereinafter referred to as being of the kind specified) comprising aplurality of stands disposed at positions spaced apart successivelyalong a feed path for the rod stock, each stand comprising a body and apair of co-operative rolls rotatably mounted on the body for rotationabout spaced parallel axes and defining therebetween an aperture on thefeed path for the passage of the stock to be rolled.

The term rod stock as used herein is to be deemed to mean elongatedstock of any cross-sectional shape. The invention has, however, beendeveloped primarily in relation to the rolling of rod stock of circularshape in crosssection and has certain advantages, as hereinafter moreparticularly pointed out, in relation to rolling mills of the kindspecified wherein the rolls are formed to produce rod stock of thiscross-sectional shape.

One of the general problems which is encountered in rolling rod stockaccurately to specified cross-sectional dimensions is that a variety ofcauses give rise to factors producing a random, or systemmatic,variation in the load applied by the rolls to the rod stock undergoingrolling `in a direction inwardly of the aperture, and such variationresults in corresponding variation in at least one dimension of theaperture, leading ultimately to the 1inished product (i.e. the rolledrod stock) departing from the specified cross-sectional dimensions towhich such stock is required to be rolled.

In stands of conventional construction employed in rolling mills of thekind specified, the rolls are supported at their ends in bearingassemblies which, for one of the rolls at least, are mounted fortranslatory movement in the body of the stand in a direction towards andaway from the other roll so as to allow the dimension of the aperture ina direction at right angles to the axes of the rolls to be varied asrequired (this dimension being generally known as, and hereinafterreferred to as, the rollway dimension).

Because wear takes place on the surface of the rolls during operation ofthe rolling mill, it is not practicable to insert rigid dimensionallyinvariable spacer blocks between corresponding bearing assemblies of thetwo rolls yof each stand. Such spacer blocks would be subjected tocompressive loading by `a head screw means operating between the body ofthe stand and the movable bearing assemblies to apply the appropriateforce to the rolls. It would be impossible to remove and insert suchspacer 3,470,722 Patented Oct. 7, 1969 blocks during operation of therolling mill, and under the conditions of operation it would be'impossible reliably to select the particular dimension of a freshspacer block to be substituted in order to maintain the rollwaydimension of the aperture at the required value, even if removal andinsertion of such blocks could be contrived.

Consequently the rollway dimension is determined Wholly by a balance offorces, namely the force exerted by the head screw means tending todecrease the rollway dimension of the aperture, and an opposing reactiveforce exerted by the stock for the time being situated in the aperture.

The reactive force can vary due, for example, to changes in thecomposition of the stock and changes in its cross-sectional dimensionsparallel to the rollway dimension which may occur lin a random orsystematic manner.

The problem of maintaining a constant rollway dimension is even moreserious in multi-strand mills where a plurality of strands of rod stock(usually two) are fed side-by-side along the feed path simultaneouslybetween axially spaced portions of the rolls. In this case there isusually a short gap between the trailing end of one piece of rod stock(formed from a given billet) and the leading end of the succeeding pieceof rod stock (formed from a succeeding billet) but this gap in onestrand of the rod stock does not necessarily coincide longitudinallywith the corresponding gap in the other strand of rod stock (assumingthe mill to be one designed for two-strand rolling). Consequently thereactive forces exerted by the rod stock (which tends to separate therolls) is very substantially diminished when a gap is present in onestrand and the whole of the reactive force is exerted by the otherstrand. As a result of this the rollway dimension decreases. There isconsequently a decrease in the rollway dimension of the other (ungapped)strand and although there is some increase in the dimension of thisstrand in a direction parallel to the axis of the rolls (this dimensionbeing known generally as, and hereinafter termed the guideway dimension)such increase is less than would maintain the cross-section or area ofthe strand at the value which it would normally have on exit from therolls. In other words the decrease in rollway dimension producesadditional elongation of the strand as well as some increase in guidewaydimension.

In rolling rod stock to circular cross-section it is usual for thestands excepting the last two or three in the series to effect reductionin the cross-sectional area of the stock by rolling it to ovalcross-section. rl`his may be done only in alternate stands of theseries, lthe intervening stands serving to roll the stock back tocircular crossasection or approximately to this shape. Alternatively,however, each stand in the series (other than the last two or three) mayroll the stock to oval cross-section in which case the rollway dimensionis always that of the minor axis of the oval section and devices arethen provided in between successive stands to twist the emerging ovalsection of the stock angularly about its own axis through before itenters the next stand. The decrease from the proper value of the rollwayldimension from the causes previously mentioned can produce necking,that is to say local decrease of the cross-section area of the stock ateach stand Where such rollway dimension is so decreased.

The last stand or possibly the last two or three stands have rollapertures which are shaped in conformity with the desiredcross-sectional shape of the finished product and the necking of thestock which has taken place in passage through preceding stands can leadin the last stage to the production of stock which is necked, that is tosay below its proper cross-sectional area or which fails to conform tothe specified rollway and guideway dimensions 0r deviates from thedesired specification in both these respects.

The object of the present invention is to avoid or reduce thesedisadvantages.

According to the present invention we provide, for a rolling mill of thekind specified, a stiffness controlling unit comprising a jack having ablock-like body and a movable thrust element in combination defining achamber containing, or adapted to contain, la selected volume of a solidstate medium conformable to the shape of the chamber when under pressureand having the compressibility characteristics of a liquid, the jackbeing adapted for mounting on or in the body of an associated one of thestands in a position such that its thrust element partakes of the stressset up in the body of the stand in response to the establishment ofapplied load urging rolls towards each other to decrease the rollwaydimension, the selected volume of the medium determining the stiffnessof the unit and hence that of the stand in which it is adapted to bemounted.

The stiffness characteristics of the jack include two components; afirst component which is invariable for any particular jack and isdetermined by the wall thickness of the portion of the body whichdefines the chamber, the wall thickness of the thrust element, thematerials of which these components are made, and the kind of medium inthe chamber; and a second component which is variable and dependent onthe volume of the medium in the chamber.

Such jack may be made conveniently of dimensions enabling it to bemounted or inserted between a bearing assembly of one of the rolls,which assembly is itself movable relatively to the body of theassociated stand to vary the rollway dimension, and an abutment so thatcompressive loading is exerted between the thrust faces of the jack assuch bearing assembly is moved in a direction to decrease the rollwaydimension. Thus, for example, the jack may be inserted betweencorresponding bearing assemblies of the two rolls of the stand atadjacent ends of the rolls, so that it opposes movement of the rollstowards each other and applies a reactive force supplementing that ofthe stock when disposed in the aperture between the rolls.

As thus applied the jack increases the effective stiffness of the stand.The term stiffness as used herein means the change in applied loadrequired to produce unit change in rollway dimension, such load beingmeasured in the case of the jack in the absence of any stock in theaperture between the rolls.

The stiffness of the jack may be made equal, or approximately equal, tothe stiffness presented by the stand itself.

It has previously been proposed to control the rollway dimension bymeans of hydraulic jacks inserted between the bearing assemblies of therolls in stands of a rolling mill, but according to these proposals thejacks are merely used to adjust the separation of the bearing assembliesin response to measured variations in the rollway dimension orparameters related thereto, and such adjustment is achieved by extendingor contracting the jacks to the appropriate extent, Thus according tothese proposals the rollway dimension is continuously monitored and theseparation of opposed thrust faces presented by the jack con- :erned iscontinuously adjusted to compensate for any observed variations.

The present invention makes use of an entirely different zoncept. Thestiffness of stands in rolling mills is adiusted to a pre-set valuedependent on the function of the stand concerned by means of jacks,which are self contained units. The stiffness of such a jack is adjustedby the selection of an appropriate volume of the medium in the chamber,and once adjusted the stiffness of the jack remains unchanged so long asthe function of the stand in which it is inserted remains unchanged.

It is contemplated that jacks as hereinbefore described may be employedin some or all of the stands of a rolling mill other than the last orthe last group of stands, for the purpose of increasing the effectivestiffness of the stands and thereby minimising any decrease which mayoccur in the rollway dimension of the stand concerned in consequence ofa reduction in counterthrust exerted by the stock tending to decreasethe separation of the rolls.

In the case of the last stand, or possibly the last two or three stands,where the apertures defined by the rolls thereof are shaped inconformity with the desired crosssectional shape of the nished productrequired to be produced, the jack may be mounted or inserted in or onthe body of the stand concerned in a position such that the load appliedto the movable roll is applied effectively through the intermediary ofthe jack. In this case the stiffness of the jack would be selected to beless than the stiffness of the stand without the jack. This feature ofthe invention provides an improved compromise in departures fromdimensional tolerance as between the rollway dimension and the guidewaydimension of the stock emergent from any such stand so equipped.

The invention also resides in a method of rolling rod stock by passingsaid stock through a rolling mill of the kind specified characterised inthat at least one of the stands, of which the rolls define an aperturehaving dimensions other than those of the desired cross-sectional shapeof the finished product required to be produced, has its stiffnessincreased to a predetermined extent by means of such a stiffness controlunit.

At least one of the stands, of which the rolls define an aperture shapedin conformity with the desired crosssectional shape of the finishedproduct required to be produced, may have its stiffness decreased to apredetermined extent by means of such a stiffness control unit.

The invention will now be described, by way of example, with referenceto the accompanying drawings wherein:

FIGURE 1 is a diagrammatic view in side elevation of a rolling mill ofthe kind specified which in accordance with the invention is equippedwith stiffness controlling units;

FIGURE 2 is a diagrammatic view in front elevation of first stand of therolling mill illustrating the position in which the stiffnesscontrolling units are mounted therein, the other early stands beingsimilar;

FIGURE 3 is a view similar to FIGURE 2 showing the last stand of therolling mill and illustrating the position in which the stiffnesscontrol units are applied thereto, the other later stands being similar;

FIGURE 4 is a graph illustrating the operation of the arrangement shownin FIGURE 2;

FIGURE 5 is a graph illustrating the operation of the arrangement shownin FIGURE 3;

FIGURE 6` is a plan view of one of the stiffness con-v trol units shownpartly in cross-section in the line VI-VI of FIGURES 7 and 8;

FIGURE 7 is a view of the same unit in cross-section on the line VlI-VIIof FIGURE 6;

FIGURE 8 is a view of the same unit in cross-section of the lineVIII-VIII of FIGURE 6;

FIGURE 9 shows a further type of stiffness control unit in medialcross-section; and

FIGURE l0 is a graph illustrating typical stiffness characteristics of astiffness control unit.

Referring firstly to FIGURE l, the rolling mill is of the multi-strandtype incorporating a plurality of stands of which the first two, 10 and11, and the last two, 12 and 13, only are shown. The stock to be rolledmay be metal stock such, for example, as steel.

Each stand may be of any conventional construction which is notillustrated in detail, but only diagrammatically. Each stand is ofsimilar construction and the various parts of stands 10, 11, 12 and 13respectively are designated by the same numbers with sufhxes a, b, c andd. The first stand 10 includes a body in the form of a frame includingupstanding side members 14a connected at their upper ends by a headmember 15a and at their lower ends to a base 16a. The side members 14aeach incorporate a vertical guideway 17a in the form of a slot in whichare mounted lower and upper bearing assemblies 1811l and 19arespectively. Lower and upper rolls 20a and 21a are supported at each oftheir ends by bearing assemblies 18a and 19a respectively, the formerabutting the lower end of the guide slot 17a and the latter beingmovable longitudinally of the guide slot 17a to vary the rollwaydimension r of apertures 9a defined by grooves 8a in the rolls 20a and21a. Downward thrust is applied to the upper roll 21a by means ofadjustable head screws 22a which, as seen diagrammatically in FIGURE 1,exert a downward thrust directly on the upper bearing assemblies 1911and 19h of the early stands 10 and 11, and indirectly on the upperbearing assemblies 19e and 19d of the last stands 12 and 13. These headscrews 22a-d operate in threaded bores in the side members of therespective frames. Such downward thrust is normally opposed only byupward counterthrust of stock in the apertures 9a between the rolls,`apart from weight balancing means which may be employed for the upperroll.

As seen in FIGURE 2, stiffness control units 23a are inserted betweenthe bearing assemblies 18a and 19a so as to exert counterthrustassisting that exerted by the stock in the apertures 9a between therolls. As seen from FIGURE l a similar arrangement is adopted for thesecond stand 11.

As seen in FIGURE 3, stiffness control units 23d -are inserted betweenthe head screws 22d and the upper bearing assemblies 19d so that thethrust exerted by the head screws is applied to the upper roller 21detectively through the stiffness control units 23d. As seen from FIGURE1 a similar arrangement is adopted for the penultimate stand 12.

It will be understood that it is not essential that the stiffnesscontrol units should be applied between the upper and lower bearingassemblies for stands equipped similarly to that shown in FIGURE 2; theycould be applied between the upper bearing assembly and some other lxedabutment on the side member of the stand concerned. Similarly it is notessential that the stilness control units 23 in stands equippedsimilarly to that shown in FIGURE 3 should be inserted between the lowerends of the head screws and the upper bearing assemblies; they could beinserted at 4any convenient position where they will reduce theeffective stiffness of the stand concerned. For example, if the headscrews were to operate in separate nuts mounted for vertical oatingmovement between abutments in the side members of the frame, thestiffness control units could be mounted between such nuts and theabutment against which the nut presses when the screw is tightened toexert the load. Alternatively, they could be placed between each bearingsupporting the bottom roll and the underlying part of the frame.

Referring specifically to FIGURES 6 to 8 which illustrate one form ofstiness control unit in accordance with the invention, the stiffnesscontrol units 23a-d each comprise a hydraulic jack having a bodycomprising a block 24 formed with a cylindrical chamber 25. The chamber25 contains a thrust element in the form of a piston 26, preferablyhaving an upwardly presented, partspherical, concave seating as shown at27 in which a thrust block 28 having a corresponding convex seating atits underside is mounted. The upper side of the thrust block 28 servesas a thrust face 28f.

The space 29 between the piston 26 and the bottom of the chamber 25contains a liquid.

The stiffness of the jack is determined by the .materials of which thebody and thrust element are made, as well as to some extent by a sealingO ring contained in a groove in the piston 26, the dimensions of theseparts and the quantity of liquid in the chamber 29, which, of course,determines the position of the piston 26.

The amount of liquid in the space 29 can be varied by means of an inletdevice which is shown in longitudinal section in FIGURE 7 and an outletdevice which is shown in longitudinal section in FIGURE 8.

Referring now to FIGURE 7, the inlet device comprises a non-return inletvalve disposed in a cavity 51 formed as a widened portion of a bore 56extending into the block 24 from its underside, The outer end of thecavity 51 opens out into a counterbored portion and receives a plug 52,a sealing `washer 54 being trapped between the plug S2 and the shoulder55 aiorded at the inner end of the counterbored portion. The valveincludes a ball element 49 which is pressed by a spring 50 into contact`with a co-operating seating 48 afforded by the shoulder at the junctionof an inner most part of the bore 56 and the inner end of the cavity 51.

Admission of liquid to the chamber 51 of the inlet valve is by way of a.duct l47 which extends between the inner part of the bore 56 and aninlet socket 45 which is threaded internally at 46 to receive acomplementary, externally threaded, male connector. Such connector may,for example, be provided on the end of a flexible pipe from a source ofhydraulic fluid under pressure, such as a manually-operated `orpower-operated pump.

An inclined bore 53 extends from the inner end of the inlet socket 45 tothe lower part of the chamber 26 and intersects the cavity 51. Theoutlet end of this bore 53 is closed by a screw 57 and sealing washer58. Thus, when liquid is admitted to the socket 45 at a pressuresuiicient to displace the ball element 49 from its seating 48, againstthe force of the spring 50 and any liquid already in the chamber 26, theliquid can enter the space 29 by Away of the duct 47, the bore 56, thecavity 51 and the inclined bore 53.

Referring now to FIGURE 8, the outlet device includes an outlet valveincluding a ball element 32 which is -pressed on to a co-operatingseating 33 by a rigid element in the form of a thrust rod 34. Theseating 33 is formed by a shoulder at the junction of a bore 31 and awidened portion thereof formed in a valve body 59. The valve body 59 isscrewed into a recess 61 at the inner end of an outlet chamber 37, theinner end of which is sealed by a washer y60 disposed between a headportion of the valve body 59 and a shoulder around the recess 61. Thethrust rod 34 is :screw threaded and extends through an internallythreaded bore in a bush 36 which is itself screwed into the forward endof the outlet chamber 37, such bush having an external nut 38compressing a seal element 39 disposed in a rebate 40 and serving toseal the outer end of the chamber 37. The thrust rod 34 has, at itsouter end, an operating member 3S Iwhich may be cylindrical and isequipped with a sealing element in the form of an O ring 41 mounted in agroove 42 and engaging the inner face of a counterbore 43 in the bush36. A duct 30 extends between the inner end of the recess `61 and thelower part of the chamber 26. Normally the thrust rod 34 is screwedtightly into the bush 36 so that the ball element 32 is pressed firmlyinto its seating 33 and liquid is not permitted to flow from the space29. However, when the thrust rod is slackened the pressure of the liquidin the space 29 lifts the ball element from its seating and so liquidcan flow from the space 29 through the duct 30, and bore 31 into theoutlet chamber 37. A transverse duct 44 extends between the outletchamber 37 and the inlet socket 45 to allow liquid to be displaced fromthe outlet chamber 37 into the inlet socket.

In the earlier stands the stiffness of the jacks utilised is selectedwith reference solely to the rollway dimension presented by the rolls.The thrust face Zf of the thrust element 28 transmits the load to theupper bearing assembly `concerned whilst the thrust face 24f provided bythe body 24 of the jack transmits the load to the upper face of thelower bearing assembly concerned. In such cases the stiffness of thejack `comprising the relevant stiffness control units 23a and b may beapproximately the same as the stiffness of the stand and this producesapproximately 100% improvement in variation of the rollway dimension asa result of any change in the component of counterthrust exerted by thestock (neglecting roll bending and deflection occurring internally ofthe bearings).

This is illustrated in FIGURE 4 in which the total load P exerted by thehead screws 22a is plotted as ordinate against rollway dimension r forthe stand and the stiffness control units 23a separately.

Curve A represents the relationship between load P and dimension r forthe stand alone (assuming the stiffness control units to be absent) andcurve B represents the same relationship with respect to the stiffnesscontrol units (assuming no dimensional changes in the stand).

Assuming that on the curve A the point a1 represents operatingconditions at any given instant, the component of counterthrust suppliedby the stiffness control units has a Value p1 and the component `ofc-ounterthrust supplied from the stock is then pz-pl where p2 is thetotal thrust applied by the head screws.

Assuming that the rolling mill is a two-strand mill, and that a gapoccurs between the leading and trailing ends of successive pieces ofstock forming one strand, the component of counterthrust supplied by thestock may then decrease to move the working point to a new position a2in which the component of c-ounterthrust supplied by the stiffnesscontrol units 23a is now p3, where p3 is greater than p1, and the thrustsupplied by the head screws is p4 which is less than p2.

In the absence of the stiffness control units the working point wouldhave become displaced to a position a3 such that the thrust p5 appliedby the head screws would be equal to p4-(p3-p1), assuming that theslopes of the curves A and B in the vworking region are equal and ofopposite sign (as would be the case when the stiffness control unitsafford collectively the same stiffness as the frame).

The proportional reduction in change of rollway dimension is fwhere/'2=2r1. It will be evident that a higher percentage in the reduction ofr can be obtained by increasing the stiffness of the units 23 (that isto say the negative slope of curve B) as desired.

The stock passing into the last stand 13 will normally have an ovalcross-section arranged `with its major dimension vertical, ie. parallelto the rollway dimension of the stand 13, this being achieved by theprovision of a known twisting device (not shown) between the stands.Similar devices will -be provided between each of the other pairs ofadjacent stands.

If the stiffness control units 23d provided in the stand 13 were placedin the same positions as those shown in FIGURE 2, to increase theeffective stiffness of this stand, the rollway dimension of the stockemergent from the stand 13 would acquire improved accuracy as to anydeparture from the specified dimension but the guideway dimension of thestock may exhibit an increased departure from the specified dimensionmerely in consequence of the improvement brought about in the accuracyin the rollway dimension.

Accordingly, improved overall results, taking into consideration theaccuracy of the stock in both the rollway and guideway dimensions, areachieved by designedly decreasing the effective stiffness of the laststand 13 and possibly of the penultimate stand 12 also, as shown.

For this purpose stiffness control units 23d in the last stand 13 areinserted in the position already described and shown in FIGURE 3. Herethe thrust face of the thrust element transmits the load to the headscrew con- 8 v cerned; whilst the thrust face afforded by the body ofthe jack transmits the load to the upper face of the upper bearingassembly concerned. As also mentioned previously the units could bearranged between the lower bearing blocks 18d and the part of the bodyof the stand 13 on which such blocks are supported. A similar result isachieved in either case.

The characteristic representing operation is shown graphically in FIGURE5 in which the load p exerted by the head screws 2.3 is plotted asordinate against change of dimensions of the stand and stiffness controlunits.

The curve A represents, as in FIGURE 4, the characteristics of the standas suchjwhilst curve B represents the characteristics of the stiffnesscontrol units. In this case the effective stiffness is the combinedstiffness represented by curve C having a lower value than either thestiffness of the stand or the stiffness control unit.

The operating charactistics of the stand, with regard to variation ofrollway dimensions, are shown in respect of a reduction of load from avoltage p6 to p7. This produces a shift of the 4working point from a6 toa7 and results in a change of rollway dimension of r3. The correspondingchange with respect to the curve C is from a4 to a5, the change ofrollway dimension in this case being am which is greater than ra. Theincrease in 5r produces a corresponding decrease in the change ofguideway dimensions, thus achieving an improvement in the accuracy ofthe means cross-sectional dimensions of the finished product.

When the jack is used to increase the effective stiffness of the standand change in the quantity of liquid in the chamber is effected, for thepurpose of changing the effective dimensions of the jack between thethrust faces, some variation in the stiffness of the jack itself willoccur. This latter variation may be confined to a limited range byproviding a mechanical adjustment means on, or in association with, thejack. Such means may comprise an assembly of shims or packing piecesbetween one of the thrust faces and the part of the mill stand againstwhich this face would otherwise lean. When the jack is used to decreasethe stiffness desired variation in the latter is effected by changingthe quantity of liquid in the chamber. Dimensional variations betweenthe thrust faces consequent on this are not important since they can beaccommodated by the head screw means of the mill stand.

It is important to note that once the jack is installed it will notnormally require further adjustment unless or until the function of thestand itself is changed. The quantity of liquid in the chamber isadjusted in accordance with the requirements of the stand in which it isinstalled, and is not varied by external means to accommodate orcompensate transistory changes in the rollway dimension. Thus the unitis self contained and preset to provide the requisite increase ordecrease in the stiffness of the stand, although it can readily bere-set when necessary to provide different characteristics.

An alternative form of stiffness control unit is illustrated in FIGURE9. This form of unit has been developed particularly for use in the laststand 13, or one of the last stands, where it is desired to decrease thestiffness of such stand. However, it could be employed in the earlierstands.

The alternative unit as shown in FIGURE 9 is of generally simplerconstruction than that shown in FIGURES 6 to 8, and employs a solidstate medium instead of a liquid to obtain the desired stiffnesscharacteristics. This unit comprises a cylindrical block-like body 74having a cylindrical chamber 75 therein. This chamber 75 opens out intothe upper end of the body 74 and has a slightly flared mouth asindicated at 80. At the lower end of the body 74- is formed with aradial bore 81 extending inwardly from its cylindrical side face andintersecting an inclined bore 82 which leads from the lower end of thechamber 75.

A block 83 of rubber, or other similar material which hascompressibility characteristics similar to a liquid when totallyenclosed, is arranged within the chamber 75.

The block 83 is shaped approximately into conformity with the chamber75, i.e. is generally cylindrical, but need not -be made as an exact orclose t therein since it will readily conform to the shape or" thechamber when it is compressed.

The height or thickness of the block 83 is selected according to therequired stilfness of the unit as a whole.

The block 83 is compressed in the chamber 75 by a thrust elementcomprising a piston 76, the block occupying the entire space bounded bythe walls of the chamber and the piston in combination. The piston 76 isgenerally cylindrical and has a plain lower end face 77 which contactsthe upper face of the solid rubber block 83. The upper end of the piston76 is formed to provide a head 78 having a part-spherical thrust face78j, the head 78 being of approximately the same diameter as that of thebody 74.

The axial length of the piston 76 received within the chamber 75 issuch, in comparison with the axial length of the chamber 75 and theheight of the rubber block 83, that the latter is compressed fully intoconformity with the shape of tlhe cylinder by downward movement lof thepiston under applied load before the Iunderside of the head 78 can abutthe mpper end of the body 74.

Any air trapped between the underside of the rubber block 83 and thebottom of the chamber 7S is expelled through the passageway afforded bythe bores 81 and 82 as the block is compressed. Similarly any airbetween the lower end of the piston 76 and the upper side of the rubberblock can escape between the piston and the cylinder wall of the chamber75. Although the piston is a close sliding t within the chamber 75 thereis suiiicient clearance to allow air to escape in this way.

However, the piston is formed with a chamfered edge 84 around its lowerend face 77 so that when the rubber block 83 is compressed the medium isformed into the annular space afforded around the face 77 so as to sealthe chamber completely.

The stiffness of such a unit may be varied with comparatively narrowlimits by replacing the rubber block 83 by a block of differentthickness. In general however the stiffness of such a unit would not bealtered once the unit was assembled, and a range of such units wouldnormally be available, each unit having a speciied stiffness.

FIGURE illustrates the stiffness characteristics of a typical jack. Thedepth of liquid, or the thickness of the rubber block, in the chamber isplotted as ordinate (the units being inches) and the reciprocal of thestiifness of the unit, or displacement of the thrust element, is plottedas abscissa in units of thousands of an inch per ton of applied load.

From this it will be seen that the compressibility of the unit increaseswith increase in the amount of the medium (solid or liquid) in thechamber, i.e. the stiffness is inversely related to the volume of themedium. Thus, by selecting the amount of liquid or the size of therubber block in the chamber a unit of predetermined stiffness can beobtained.

What we claim is:

1. Stiifness control means for a rolling mill stand ncluding a pair ofco-operating rolls, such means comprising a hydraulic jack having:

(a) a block-like body,

(b) a movable thrust element,

(c) a chamber defined by said body and said thrust element incombination,

(d) means for mounting said body in said stand in a position such thatsaid thrust element partakes of stress set up in said stand in responseto establishment of applied load urging said rolls towards each other,and

(e) said chamber containing a selected volume of a solid state mediumwhich is conformable to the shape of said chamber when underI pressureand having the compressibility characteristics of a liquid, and theselected volume of said medium determining the stiffness of thestiffness control means and hence that of said stand in which it is tobe mounted.

2. The structure according to claim 1 wherein said block-like bodyincludes means for permitting the escape of air from said chamber.

3. The structure according to claim 1 wherein said medium comprises asolid block of rubber.

4. A multiple strand rolling mill stand for simultaneously rolling atleast two strands of rod-stock and comprising:

(a) a stand body,

(b) a pair of co-operative rolls at least one of which is movabletowards and away from the other and each of which is formed with atleast two axially lspaced peripheral grooves which in combination withthe respective grooves of the other roll dene respective apertures,

(c) a pair of respective bearing assembles at each end of said pair ofrolls,

(d) means for applying a load to said movable roll to urge the lattertowards the other rolls, and

(e) means for controlling the stiffness of the stand comprising a pairof independent yieldable units each having a stiffness of tihe sameorder as that of the stand mounted in said stand body in associationwith said respective pairs of bearing assemblies in a fposition such asto partake of stress set u-p in said stand in response to establishmentof applied load urging said rolls towards each other.

5. The structure according to claim 4 wherein said apertures havedimensions other than those of the desired cross-sectional shape of therolled rod stock required to be produced, and said stiffness controlunits are disposed between respective abutments fixed to said stand bodyand each of said bearing assemblies of said movable roll on the side ofthe latter remote from that at which said load is applied whereby theeffective stiifness of the stand is increased.

6. The structure according to claim 4 wherein said apertures havedimensions conforming with the desired cross-sectional shape of therolled rod stock required to be produced, and said stiffness controlunits are disposed between each of said bearing assemblies of saidmovable roll and said means for applying said load to the latter wherebythe effective stiifness of the stand is decreased.

7. The structure according to claim 4 wherein said stiffness controlunits each comprise,

(a) a block-like body,

(b) a movable thrust element, and

(c) a totally enclosed chamber dened by said body and said thrustelement in combination and containing a preselected volume of a mediumwhich is conformable to the shape of said chamber when under pressureand has the compressibility characteristics of a liquid, said selectedvolume of said medium determining the stiffness of the stiifness controlmeans and hence that of said stand.

8. The structure according to claim 7 wherein said medium contained insaid chamber of said stiifness control unit comprises a liquid, and saidstiffness control means further comprises,

(a) means for admission of a variable, selected, quantity of said liquidinto said chamber so as to enable adjustment of the effective stiffnessof said stiffness control unit, and

(b) releasable means for preventing release of said liquid from saidchamber so that said quantity of said liquid therein can be xed at anyselected value.

9. The structure according to claim 7 wherein said medium in saidchamber of said stiiness control means comprises a solid state medium.

10. The structure according to claim 9 wherein said block-like body ofsaid stiffness control means includes means for permitting the escape ofair from said chamber whilst the latter is electively totally enclosedagainst escape of said solid state medium therefrom.

11. The structure laccording to claim 9 wherein said medium comprises ablock of rubber.

12. In a rolling mill for rolling rod stock and comprising a pluralityof rolling mill stands arranged in a line to be traversed successivelyby said rod stock wherein each stand comprises,

(a) a stand body,

(b) a pair of co-operative rolls at least one of which is movabletowards the other and each of which is formed with a peripheral groovewhich in combination dene an aperture,

(c) a pair of respective bearing assemblies at each end of each of saidpair of rolls, and

(d) means for applying a load to said movable roll to urge the lattertowards the other roll,

and wherein,

(e) in all of said stands except the last stand in the line saidaperture has dimensions other than those of the desired cross-sectionalshape of the rolled rod stock required to be produced, and in said laststand in said line said aperture has dimensions conforming with thedesired cross-sectional shape of the rolled rod stock required to beproduced,

the improvement comprising,

(f) means for decreasing the stiiTness of said last stand comprising apair of yieldable units each having a stiffness of the same order asthat of the stand mounted between said bearing assemblies of saidmovable roll and said means for applying load thereto, and

(g) means for increasing the stilness of at least one of said standswherein said aperture has dimensions other than those of the desiredcross-sectional shape of the rolled rod stock required to be produced,comprising a pair of yieldable units each having a stiffness of the sameorder as that of the stand mounted between respective abutments xedrelative to said stand body and said bearing assemblies of said movableroll on the side of the latter remote from that .at which said load isapplied thereto.

13. In a multiple strand rolling mill for simultaneously rolling atleast two strands of rod stock and comprising a plurality of rollingmill stands arranged in a line to be traversed successively by said rodstock wherein each stand comprises,

(a) a stand body,

(b) a pair of co-operative rolls at least one of which is movabletowards the other and each of which is formed with at least two axiallyspaced peripheral grooves which in combination with the respectivegrooves of the other roll dene respective apertures,

(c) a pair of respective bearing assemblies at each end of each of saidpair of rolls, and

(d) means for ,applying a load to said movable roll to urge the lattertowards the other roll,

and wherein,

(e) in all of said stands except the last stand in the 12 v line saidapertures have dimensions other than those of the desiredcross-sectional shape of the rolled rod stock required to be produced,and in said last stand in said line said apertures have dimensionsconforming with the desired cross-sectional shape of the rolled rodstock required 'to be produced,

the improvement comprising,

(f) means for decreasing the stiffness of said last stand comprising apair of independent yieldable units each having a stiffness of the sameorder as that of the stand mounted between said bearing assemblies ofsaid movable roll and said means for applying load thereto, and y (g)means for increasing the stiifness of at least one of said standswherein said apertures have dimensions other than those of the desiredcross-sectional shape of the rolled rod stock required to be produced,comprising a pair of independent yieldable units each having a stillnessof the same order as that of the stand mounted between respectivelabutments xed relative to said stand body and said bearing assembliesof said movable roll on the side of the latter remote from that at whichsaid load is applied thereto.

14. A method of rolling rod stock by subjecting said stock to aplurality of successive rolling operations and a nal rolling operationbetween respective pairs of rolls journalled in respective mill standsfor rotation about respective pairs of parallel axes of rotation to formrolled rod stock having a preselected rollway dimension in a directionat right-angles to said axes of rotation and also a preselected guidewaydimension in a direction parallel to said axes of rotation, each of saidpairs of rolls deining in combination a respective aperture throughwhich said stock is passed to alter its cross-section, wherein theimprovement comprises controlling the rollway dimension of said stockduring said nal rolling operation less closely than during saidsuccessive rolling operations preceding said inal rolling operation bydecreasing the effective stiffness of said mill stand in which saidfinal operation is carried out.

15. A method of rolling rod stock according to claim 14 wherein therollway dimension of said stock is controlled during at least one ofsaid successive rolling operations preceding said iinal rollingoperation by increasing the effective stiffness of said mill stand inwhich said operation is carried out.

References Cited UNITED STATES PATENTS 2,796,253 6/ 1957 Schulze et a1.267--1 3,059,914 10/1962 Williamson 267-1 3,197,986 8/1965 Freedman etal. 72--16 3,272,491 9/ 1966 Knittel 267-1 3,290,034 12/1966 Williamson267-1 3,314,263 4/1967 Hill 72-237 3,339,393 9/1967 Rice 72-2463,024,679 3/1962 Fox 72-245 CHARLES W. LANHAM, Primary Examiner B. I.MUSTAIKIS, Assistant Examiner U.S. C1. X.R.

